Heretofore, as a snow melting device to be used for a greenhouse for helping to cultivate plants, there has been known a snow melting device, wherein a spraying pipe is disposed on an exterior side of the roof of a greenhouse, and groundwater or warm water is supplied and is sprayed out (e.g., JP-A-63-263021). However, this device has a problem in that unless water is discharged from the spraying pipe at, e.g., nights in winter, the water is frozen to damage the spraying pipe since the spraying pipe is exposed outdoor.
There has been also known a snow removing device, wherein snow on a sloping roof is slipped down toward a gutter, and the slipped snow is melted by a snow melting means disposed near to the gutter (e.g., JP-A-9-107806). This device utilizes a system, wherein a pile of snow on the roof is slipped down by heating the interior of a greenhouse by an air conditioner to warm the roof made of a covering material (such as a glass sheet or a rigid synthetic resin plate), melting the pile of snow on the roof and gradually moving down the melted snow toward the gutter along the roof. In this system, a hot water pipe and a warm water pipe having apertures formed therein are disposed in the gutter of this device, hot water is passed through the hot water pipe to destroy a snow bridge, and warm water is spouted from the apertures of the warm water pipe to melt the snow. The roof is formed by a plate, which has a single structure. The heat source for melting a pile of snow on the roof is the warm air in the greenhouse. This system has caused, e.g., problems that nozzles are frozen, that snow is accumulated in a tunnel shape above the gutter since nozzles fail to melt all the snow, that snow is insufficiently melted, that nozzles are clogged by dust and dirt, and that a powerful pump is needed since snow is melted by water, not air.
Additionally, there has been proposed a snow melting device, wherein a gutter is mounted in a valley portion between adjacent roofs of a multi-ridge house, a warm water circulating pipe is disposed in the gutter, and a warm air duct is disposed in the house in the vicinity of the valley portion to blow out warm air toward the valley portion (e.g., JP-A-11-243789). According to this device, snow, which has piled on the roofs covered with a plastic film, is melted by warm air in the greenhouse heated by a warm air blowing heater, and the melted snow is slipped down on the smooth film. Although a portion of the slipped snow stays in the gutter, that portion is drained along the gutter, being melted by the warm water circulating in the warm water pipe. When warm air is supplementarily blown out toward the film, a portion of the snow, which is located above the gutter and has a hollow portion formed therein, can be easily melted, which is effective to completely melt the snow or to melt the snow rapidly. Each of the roofs is formed by a plate, which has a single structure. The heat source for melting a pile of snow on the roof is the warm air in the greenhouse. However, this device has caused, e.g., problems that snow is insufficiently melted since the warm air is locally blown out, a powerful pump is needed to sufficiently melt the snow, and the pipe is frozen.
The abstract of lectures at the joint convention of the Society of Agricultural Meteorology of Japan, National Convention 2000 and the Japanese Society of Environmental Control in Biology, National Convention 2000 refers to, at pages 450 to 451, a house having a pneumatic structure roof and utilizing solar energy. It is described that the pneumatic structure roof is adopted for the purpose of ensuring a structural strength without drastically decreasing the daylight entering the house. However, it is not described that warm air is supplied in the pneumatic structure roof, i.e., the roof formed in a bag-like structure, and the air supplied into the bag-like roof is discharged. In other words, the air in the pneumatic structure roof is not effective in terms of heat insulation and of keeping the house warm since the air is not warm. When snow has piled on the roof, it is impossible to expect to obtain an effect to melt the snow.